The present invention relates to polyamide ligand-containing polymeric resins which are polymerized and/or crosslinked and methods of using the same for removing, separating, and/or concentrating certain desired metal ions from solutions, even when the desired ions are in the presence of other metal ions and/or hydrogen ions at much higher concentrations.
Effective methods for the separation and recovery of particular ions such as the transition, post-transition, and alkaline earth metal ions from solution mixtures containing these and other metal ions are of great importance in modern technology. Particularly, it is difficult to separate and recover certain metal ions such as Cd2+, Pb2+, Ag+, Ni2+, Co2+, Fe3+, Cu2+, Sr2+, and/or Ca2+ from the presence of even moderate amounts of hydrogen ion (H+). It is also very difficult to remove these desired metal ions when present at low concentrations in solutions that contain other, non-desired metal ions at much greater concentrations. Thus, there is a real need for a composition of matter and an associated method that may be used for selectively separating certain transition, post-transition, and alkaline earth metal ions from other non-desirable ions.
It is known that ethylenediaminetetraacetamide (EDTAA), diethylenetriaminepentaacetamide (DTPAA), and nitrilotriacetamide (NTAA) form strong complexes with various metal ions in solution. These molecules may be shown as Formulas 1-3 respectively below: 
J. M. Grana-Molares, C. Baluja-Santos, A. Alvarez-Devesa and F. Bermejo-Martinez, Etude Spectrophotometrigue des Complexes du Cobalt(III) avec les Amides de l""EDTA et du DTPA, Analysis, Volume 7, 249-252 (1979) reported on the synthesis of EDTAA and DTPAA and their ability to complex Co(III) as shown by a spectrophotometric technique. In a different study, L. Przyborowski, Complex Compounds of Amides and Thioamides of Aminopolycarboxylic Acids, Part III. Synthesis, Properties and Copper(II) Complexes of Nitrilotriacetotriamide and Ethylenediaminetetraacetotetraamide, Roczniki Chemii, Volume 44, 1883-1893 (1970) showed that NTAA and EDTAA could be prepared by modifying known methods and that Cu(II) formed strong complexes with NTAA.
More recently, a great deal of research has been done in the synthesis and metal ion complexation properties of polyamide-containing azacrown ethers such as those containing acetamide, propionamide, and peptide side arms. R. Kataky, K. E. Matthes, P. E. Nicholson, D. Parker and H-J. Buschmann, Synthesis and Binding Properties of Amide-Functionalized Polyazamacrocycles, Journal of the Chemical Society, Perkin Transactions 2, 1425-1432 (1990) reported on the synthesis and complexation properties of per-N-(dimethylacetamido)-substituted triaza-9-crown-3, aza-12-crown-4, diaza-12-crown-4, and tetraaza-12-crown-4. The ligating agents 1,4,7,10-tetrakis(N,N-dimethylacetamido)-1,4,7,10-tetraazacyclododecane and 1,7-dioxo-4,10-bis(N,N-dimethylacetamido)-4,10-diazacyclododecane are two chemical structures that were synthesized and which are representative of polyamide-containing ligating agents of the present invention. These ligating agents are shown respectively below in Formulas 4 and 5: 
The diamide of Formula 5 was shown to form complexes with all of the alkali metal and alkaline earth metal cations. Further, this diamide was shown to have significant selectivity for Ca2+ over the other cations studied. However, a diamide similar to that of Formula 5, but containing one more methylene group in each amide-containing arm (thus, having two N,N-dimethylpropioamido substituents), was shown to form weaker complexes with these same metal ions.
Further studies of amide ligands, such as those depicted by formulas 4 and 5, have concluded that the size of the metal ion-ligand chelate ring determines the strength of the interaction between the ligand and the metal ions. For example, a five-membered ring favored the smaller cations over a six-membered ring. Representative of fully chelated metals (Me) having five- and six-membered amide rings attached are shown in Formulas 6 and 7 respectively below: 
H. Maumela, R. D. Hancock, L. Carlton, and J. H. Reibenspies and K. P. Wainwright, The Amide Oxygen as a Donor Group. Metal Ion Complexing Properties of Tetra-N-Acetamide Substituted Cyclen: A Crystallographic, NMR, Molecular Mechanics and Thermodynamic Study, Journal of the American Chemical Society, Volume 117, 6698-6707 (1995), reported the synthesis of 1,4,7,10-tetraazacyclododecane (DOTAM) which is the unsubstituted amide analogue of the tetraamide of Formula 4. DOTAM is capable of forming complexes with a host of metal ions including many transition and post-transition metal ions. DOTAM also forms strong complexes with Cd2+ and Pb2+, even at pH levels of as low as 0.3 which is equivalent to a hydrogen ion concentration of 0.5 Molar. DOTAM may be represented by Formula 8 below: 
The articles cited above disclose procedures for synthesizing and demonstrating limited useful complexation properties of polyamide-containing ligand molecules. However, researchers have not previously been able to incorporate polyamide-containing ligands into solid phase separation systems. This is significant because these polyamide-containing ligands merely act as a solute in solution by completing with selected ions, but provide no effective means for ion separation.
The use of polymeric resins for selective removal of ions is not a new concept of itself. In U.S. Pat. No. 5,656,702, the use of poly(hydroxyarylene) polymeric resins is disclosed for removing alkali metals, particularly cesium, from industrial streams. However, never before have polyamide ligand-containing polymeric resins been successfully synthesized that can be used in a solid phase separation system to concentrate and remove desired metal ions such as members selected from the group consisting of Cd2+, Pb2+, Ag+, Ni2+, Co2+, Fe3+, Cu2+, Sr2+, and/or Ca2+ from source solutions.
The present invention is drawn to polyamide ligand-containing polymeric resins and methods of using the same for removing, separating, and/or concentrating certain desired divalent metal ions including transition, post-transition, and alkaline earth metal ions from source solutions. The unique composition of matter of this invention is a polyamide ligand-containing polymeric resin which has been polymerized and/or crosslinked. These resins are generally a reaction product of a hydroxymethylated polyamide ligand and a polymerization and/or crosslinking agent. Specifically, the polymeric resins of the present invention are comprised of from 10 to 50,000 polyamide ligand units wherein each polyamide ligand unit is defined by three or more amide groups, preferably from three to eight amide groups, and two or more amine nitrogen donor atoms separated by at least two carbons.
The present invention is particularly useful for the removing of ions selected from the group consisting of Cd2+, Pb2+, Ag+, Ni2+, Co2+, Fe3+, Cu2+, Sr2+, Ca2+, and combinations thereof from source solutions. This is true whether the desired ions are present at very low or very high concentrations, i.e., from ppb to g/l.
The concentration of desired ions is accomplished by forming a complex of desired ions with the polyamide ligand-containing polymeric resins by flowing a source solution containing the desired ions through a column packed with the polymeric resin beads or granules. The metal ion and the polyamide ligand-containing polymeric resins are then decoupled by flowing a receiving liquid through the column (in much smaller volume than the volume of source solution passed through the column) to removing, separating, and/or concentrating the desired ions in the receiving liquid solution. The receiving liquid or recovery solution forms a stronger complex with the desired ions than does the polyamide ligand-containing polymeric resins, or alternatively, temporarily forms a stronger interaction with the polyamide ligand-containing polymeric resins than does the desired metal ions. In either case, the desired metal ions are quantitatively stripped from the polyamide ligand-containing polymeric resins in a concentrated form in the receiving solution. The recovery of desired ions from the receiving liquid may be accomplished by various methods commonly known in the art including evaporation, electrowinning, and precipitation among others.
The polyamide ligand-containing polymeric resins of the present invention are a reaction product of a polyamide ligand and formaldehyde or other suitable compound capable of forming a hydroxymethylated polyamide ligand. The hydroxymethylated polyamide ligand is then polymerized using a polymerization and/or crosslinking agent to form the polyamide ligand-containing polymeric resins. The polyamide ligand-containing polymeric resins of the present invention are comprised of from 10 to 50,000 polyamide ligand units wherein each polyamide ligand unit or monomer is defined by three or more amide groups, preferably from three to eight amide groups, as well as two or more amine nitrogen donor atoms separated by at least two carbons. Each amide group of the polyamide ligand unit, after hydroxymethylation, may remain hydroxymethylated or be polymerized and/or crosslinked to other polyamide ligand units through a polymerization agent or a crosslinking agent. At least one of the amide groups of the resin must be polymerized or crosslinked, preferably from two to eight.
The structure of the present invention may be represented generally by Formula 9 as follows:
(LXm)nxe2x80x83xe2x80x83Formula 9
wherein L represents the polyamide-containing ligand having three or more amide groups, preferably from three to eight amide groups, and two or more amine nitrogens separated by at least two carbons, n may be an integer from about 10 to 50,000, m is at least three, preferably from three to eight, and X may be CH2OH, CH2Oxe2x80x94, CH2xe2x80x94, a crosslinking agent, or a resulting group from polymerization with the proviso that each X group is bonded individually to L and at least one X group per polyamide ligand unit is involved in the polymerization or crosslinking.
Amide groups of the ligand which remain hydroxymethylated after polymerization are free to bind with the desired metal ions according to the present invention. However, the amide groups of the ligand which are involved in the polymerization reaction or crosslinking may also be involved in the binding of the desired metal ions. In other words, it is not the purpose of the invention to describe specifically how each of the polymeric resins complex with each specific desired ion, only that the polymeric resins described herein will bind with the desired ions also described herein.
It is to be noted that the crosslinking agents or polymerization agents that may be used and the processes of crosslinking and/or polymerization are known in the art. For example, phenols, resorcinol, fluoroglucinol, aromatic or aliphatic amines, pyrroles, indoles, nitrates, esters, ketones, and nitriles, and/or other known crosslinking agents may be used. Further, polymerization agents that may be used include bisaldehydes, polyaldehydes, dihalogens, polyhalogens, dihalogens of diacids, polyhalogens of polyacids, diesters, polyesters, anhydrides of acids, diepoxides, polyepoxides, and/or other known polymerization agents.
In one preferred embodiment, a hydroxymethylated polyamide ligand may be polymerized linearly using a polymerization agent. In a second preferred embodiment, the generally linear polymer described above may be crosslinked using a crosslinking agent. In another preferred embodiment, a hydroxymethylated polyamide ligand may be both polymerized and crosslinked using only a single polymerization/crosslinking agent. As such, one skilled in the art may utilize these known polymerization agents and crosslinking agents in any functional combination and not depart from the scope of the present invention.
Representative examples of polyamide ligands (L) that may be hydroxymethylated and then polymerized to form polyamide ligand-containing polymeric resins that have at least three amide groups and two or more amine nitrogens separated by at least two carbons include: ethylenebis(oxyethylenenitrilo) tetraacetic acid (EGTAM), diaza-18-crown-6-tetraamide, ethylenediaminetetraacetamide-N-methylenepropanetetraamine (EDTAAMT), tris(2-aminoethyl)amine pentaamide (TRENPAM), and diethylenetriaminepentaacetamide (DTPAM). This list is intended only to be representative of the possible ligands that may be used, the limiting factor being the presence of at least three amide groups, preferably from three to eight amide groups, and at least two amine nitrogens separated by two or more carbons. Further variations of these ligands may also be used. For example, tris(2-aminoethyl)amine pentaamide (TRENPAM) may be alkyl or aryl substituted. Once polymerized, the polyamide-ligand units of the present invention form beads and/or granules which may be used for ion removal, separation, and/or concentration.
As summarized above, the present invention is drawn to a novel composition of matter comprising polyamide ligand-containing polymeric resins. The present invention is also drawn to methods for the preferential removal, separation, and/or concentration of certain desired metal ions, such as certain transition, post-transition, and alkaline earth metal ions from solution. The solution from which the desired ions may be removed may contain other metal ions or hydrogen ions present at greater concentrations than the desired ions. For example, Cd2+, Pb2+, and Ag+ may be removed from acidic and or highly chelative matrices and Ni2+, Co2+, Fe3+, Cu2+, Sr2+, and Ca2+ may be removed from slightly acidic to neutral pH matrices and from chelating matrices. Moreover, the above described polyamide ligand-containing polymeric resins provide a mechanism for separating ppb to ppm levels of Cd2+ and Pb2+ from concentrated acid solution by using separation techniques and equipment generally known in the art.
The method for separating and recovering desired ions is accomplished by forming a complex of the desired ions with polyamide ligand-containing polymeric resins. Specifically, this is accomplished by flowing a source solution containing the desired ion(s) through a packed column or other known device with these polymeric resin beads or granules in order to complex or chelate the desired metal ion(s) to one or more polyamide ligand units of the polyamide ligand-containing polymeric resins. Subsequently, the desired cation which is bound to the polyamide ligand-containing polymeric resins is released by flowing a complex-breaking receiving liquid in much smaller volume than the volume of source solution originally passed through the column or other known device. This removes, separates and/or concentrates the desired ions in the receiving liquid solution by either (a) forming a stronger complex with the desired transition, post-transition, or alkaline earth metal ion(s) than do the polymeric resins, or (b) temporarily forming a stronger interaction with the polymeric resins than do the desired metal ion(s), and thus, the desired metal ion(s) are quantitatively stripped from the polyamide ligand-containing polymeric resins in concentrated form in the receiving solution. The recovery of desired metal ion(s) from the receiving liquid is accomplished by evaporation, electrowinning, precipitation or by other known methods.